// Copyright (c) 2018 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package sampler

import (
	"fmt"

	"go.uber.org/atomic"
)

// Sampler samples the requests, out of 100 sample calls,
// 100*sampleRate calls will be sampled.
type Sampler struct {
	sampleEvery int32
	numTried    *atomic.Int32
}

// NewSampler creates a new sampler with a sample rate.
func NewSampler(sampleRate float64) (*Sampler, error) {
	if sampleRate <= 0.0 || sampleRate >= 1.0 {
		return nil, fmt.Errorf("invalid sample rate %f", sampleRate)
	}
	return &Sampler{numTried: atomic.NewInt32(0), sampleEvery: int32(1.0 / sampleRate)}, nil
}

// Sample returns true when the call is sampled.
func (t *Sampler) Sample() bool {
	return (t.numTried.Inc()-1)%t.sampleEvery == 0
}
